Effect of various polishing burs on surface roughness and bacterial adhesion in pediatric zirconia crowns

Bacterial adhesion to composite resins produced by additive and subtractive manufacturing

The aim of this study was to evaluate the surface roughness and contact angle of composite resins produced by CAD/CAM milling and three-dimensional (3D) printing for permanent restorations as well as the adhesion of S. mutans and S. sanguinis bacteria to these composites. Three CAD/CAM milling composite resins (Vita Enamic-VE, Cerasmart-CE, Lava Ultimate-LU) and three 3D printing resins (Varseo Smile Crown plus-VSC, Saremco print Crowntech-SPC, Formlabs 3B Permanent crown-FLP) were selected. Twenty samples were prepared for each group. Using a contact profilometer, the surface roughness was determined, and an optical goniometer was used to quantify the contact angle. To evaluate the bacterial adhesion, composite specimens were immersed in mucin containing artificial saliva. All samples were incubated for 24 h at 37°C in 5% CO2. CFUs were determined by counting colonies after the incubation period. Surface roughness values of test samples were the highest in the Group VSC [0.46 (0.14) µm], whereas the lowest values were found in the Group LU [0.23 (0.05) µm]. There was no statistically significant difference between the groups in contact angle values (p > 0.05). The S. mutans adhesion extent on the Group SPC was statistically higher compared to all other materials with p < 0.05. For S. sanguinis, the lowest bacterial adhesion value was recorded in Group CE (3.00 × 104 CFU/ml) and statistically significant differences were found with Group VE and VSC (p < 0.05). Different digital manufacturing techniques and material compositions can affect the surface roughnesses of composite resins. All composite resin samples have hydrophobic characteristics. Microbial adhesion of the tested composite resins may be varied depending on the bacterial species. S. mutans showed much more adhesion to these materials than S. sanguinis.

A comparative study of the cutting efficiency of diamond rotary instruments with different grit sizes with a low-speed electric handpiece against zirconia specimens

STATEMENT OF PROBLEM

The use of zirconia in dentistry has increased. However, little attention has been given to the difficulty experienced by clinicians when cutting zirconia restorations intraorally. Evidence for which grit size and type of rotary instrument is best for cutting zirconia intraorally is lacking.

PURPOSE

The purpose of this in vitro study was to identify the most efficient diamond rotary instrument grit size for cutting zirconia intraorally.

MATERIAL AND METHODS

Efficiency was measured by comparing the cutting depth of each rotary instrument into zirconia, analyzing zirconia specimens for surface damage after cutting, and measuring instrument deterioration. Thirty zirconia specimens of the same measurements were used as test specimens and cut with 30 diamond rotary instruments with different grit sizes. An electric handpiece was used with constant force (1.7 N), speed (40 000 rpm), time (1 min), and water flow rate (25 mL/min) to produce comparative data. The mean cutting efficiency values were compared by analysis, and the median values were compared by the nonparametric Kruskal-Wallis test (α=.05). Each test was followed up with pair wise comparisons of the mean or median values if significance was indicated.

RESULTS

The greatest cutting depth was achieved with a fine-grit instrument with a mean cutting depth of 5.79 mm compared with 4.54 mm for the coarse-grit instrument (P=.032). The greatest damage to zirconia was done by the coarse- and supercoarse-grit instruments (both 33%), with no substrate damage by the superfine-, fine-, and medium-grit instruments. The greatest instrument deterioration was found on the supercoarse rotary instruments (9.05%). With only 3 exceptions, the power calculations were all sufficient and above 83%.

CONCLUSIONS

The fine grit rotary instrument (between 40 and 50 µm) was the most efficient, achieving the greatest cutting depth, with no detectable macroscopic damage to the zirconia and minimal instrument deterioration.

Should finishing, polishing or glazing be performed after grinding YSZ ceramics? A systematic review and meta-analysis

The present systematic review and meta-analysis aimed to assess the characteristics and consequences of post-processing methods after grinding procedures in YSZ ceramics on its surface roughness and flexural strength. The protocol of this review was made prospectively and is available online in the PROSPERO database (link). Literature searches on PubMed/MEDLINE, EMBASE, Lilacs, Web of Science and Scopus were conducted on December 2022 to select in vitro studies written in English, without publishing-date restrictions, that considered surface characteristics and mechanical properties of YSZ ceramics submitted to grinding and subsequent post-processing surface treatments as an attempt to revert the effect induced by grinding. Two authors independently selected the studies, extracted the data and assessed the risk of bias. Mean differences (Rev-Man 5.1, random effects model, α= 0.05) were obtained by comparing flexural strength and surface roughness values of ground surfaces with at least one post-processing surface treatment (global analysis). Subgroup analyses were performed considering the most prevalent categories of post-processing methods. A total of 33 (out of 4032) studies were eligible and included in the analysis. In the global analysis, ground surfaces showed higher flexural strength than when post-processing methodologies were employed (p< 0.0001). The subgroup analysis showed that only polishing was able to enhance the flexural strength after grinding (p= 0.001); however, when other protocols were used, the ground surface was always superior in terms of flexural strength (p< 0.0001). Post-processing techniques in both the global and sub-group analyses were able to reduce the surface roughness after grinding in YSZ ceramics (p< 0.00001). High heterogeneity was found in all the meta-analyses. Concerning the risk of bias analysis, the included studies had mixed scores for the considered factors. In conclusion, in terms of improving flexural strength and restoring surface roughness after grinding, polishing protocols can be considered the best indication as post-processing treatment after YSZ ceramics adjustments/grinding.

Analysis of surface characteristics of (Y, Nb)-TZP after finishing and polishing

PURPOSE

This in vitro study aimed to evaluate the surface characteristics of a full veneer crown fabricated chairside (CS) from a (Y, Nb)-TZP zirconia block in response to conventional zirconia grinding and polishing.

MATERIALS AND METHODS

Zirconia crowns (n = 40) were first prepared and divided into two groups of materials: Labside (LS) and CS, after which each specimen went through a five-step grinding and polishing procedure. Following each surface treatment, surface characteristics were analyzed using confocal laser microscopy (CLSM), average surface roughness (Ra) values were processed from the profile data through Gaussian filtering, and X-ray diffraction pattern analysis was performed to evaluate the monoclinic (M) phase content. Then, a representative specimen was selected for field-emission scanning electron microscopy (FE-SEM), followed by a final analysis of the roughness and X-ray diffraction of the specimens using the independent t-test and repeated measures analysis of variance (RM-ANOVA).

RESULTS

In every group, polishing significantly reduced the Ra values (P < .001). There was no significant difference in Ra between the polished state CS and LS. Furthermore, CLSM and FE-SEM investigations revealed that even though grain exposure was visible in CS specimens throughout the as-delivered and ground states, the exposure was reduced after polishing. Moreover, while no phase transformation was visible in the LS, phase transformation was visible in CS after every surface treatment, with the M phase content of the CS group showing a significant reduction after polishing (P < .001).

CONCLUSION

Within the limits of this study, clinically acceptable level of surface finishing of (Y, Nb)-TZP can be achieved after conventional zirconia polishing sequence.

Translucency and mechanical behavior of partially stabilized monolithic zirconia after staining, finishing procedures and artificial aging

Partially stabilized zirconia (5Y-PSZ) has been widely used to manufacture indirect monolithic restorations, and the effect of finishing procedures on the optical and mechanical properties of these materials are still unclear. The purpose of this study was to evaluate the effect of staining, polishing and glazing on surface roughness, crystalline phase content, microhardness, fracture toughness, dynamic elastic modulus, three-point flexural strength, strain distribution, color (∆E₀₀/∆L/∆a/∆b), and translucency before and after artificial accelerated aging (water spray and ultraviolet) of 5Y-PSZ. Bar-shaped and rectangle-shaped specimens of the 5Y-PSZ were prepared and divided into six groups, according to finishing procedure: GC (control), GS (staining), GG (glazing), GSG (staining and glazing), GP (polishing), GSP (staining and polishing). There was a significant difference between groups for surface roughness (p < 0.05), dynamic elastic modulus (p = 0.007), microhardness (p =  < 0.05), ∆E₀₀ (p = 0.010), and ∆a (p = 0.008). GC presented higher cubic phase content, and the stained groups (GS, GSG and GSP) presented higher monoclinic content. The different finishing procedures affected roughness, dynamic elastic modulus, microhardness, and color of 5Y-PSZ; polishing being the finish that provides minors changes to the 5Y- PSZ. Accelerated artificial aging caused color change, regardless of finishing procedure used.

Antibacterial activity improvement of dental glass-ceramic by incorporation of AgVO3 nanoparticles

OBJECTIVE

This study aimed to investigate the role of the incorporation of an antibacterial nanoceramic (AgVO₃) on the properties of a restorative dental glass-ceramic.

METHOD

A commercially available restorative glass-ceramic, commonly designated as porcelain (IPS d.SIGN) was functionalized with an antibacterial agent (nanostructured β-AgVO₃), synthesized by a hydrothermal route. Both functionalized and pristine samples were processed according to the manufacturer's instructions. All samples were characterized by X-ray diffraction, Rietveld refinement, particle size distribution, Scanning Electron Microscopy, chemical solubility, and Inductively Coupled Plasma Spectroscopy. Their antibacterial potential (Mueller-Hinton test) was analyzed against gram-positive (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli).

RESULTS

The commercial glass-ceramic showed leucite (KAlSi₂O₆) as the only detectable crystalline phase, and, for both strains, no antibacterial activity could be detected in the Mueller-Hinton agar plates test. A monophasic, needle-shaped, and nanometric β-AgVO₃ powder was successfully synthesized by a simple hydrothermal route. After thermal treatment, glass-ceramic samples containing different percentages of β-AgVO₃ showed a second crystalline phase of microline [K_0.95(AlSi₃O₈)]. For modified samples, inhibition halos were easily visible on the Mueller-Hinton test, which ranged from 11.1 ± 0.5 mm to 16.6 ± 0.5 mm and 12.7 ± 0.3 mm to 15.5 ± 0.3 mm in the S. aureus and E.coli cultures, respectively, showing that the halos formed were dose-dependent. Also, increasing the percentage of β-AgVO₃ promoted a significant increase in chemical solubility, from 72 µg/cm² (samples with 1 wt% of β-AgVO₃) to 136 µg/cm² (samples with 2 wt% of β-AgVO₃), which was associated with the silver and vanadium ions released from the glass matrix.

SIGNIFICANCE

Our in vitro results indicate that IPS d.SIGN, as most of the dental glass-ceramics, do not exhibit antibacterial activity per se. Nonetheless, in this concept test, we demonstrated that it is possible to modify dental veneering materials giving them antibacterial properties by adding at least 2 wt% of β-AgVO₃, a nanomaterial easily synthesized by a simple route.

Effects of Different Polishing Systems on Surface Roughness and Crystal Structure of Zirconia

Objective

Intraoral polishing systems have become an alternative method for reglazing, which is important to prevent or minimize rapid wear of the opposing teeth. To assess the influence of different polishing systems and duration on surface roughness and crystal structure of zirconia was compared, contributing to the preparation and effect improvement of clinical zirconia restorations.

Methods

Forty-eight zirconia specimens with equal size were fabricated by cutting and sintering zirconia discs. Then X-ray diffractometer (XRD) was adopted for examination of the specimens. Six specimens were selected as the grinding-polishing group (GL) after polishing, grinding, and glazing. Then six specimens were randomly selected from the remaining specimens as the grinding-unpolished group (GR) after surface conditioning by dental diamond burs. Subsequently, based on different polishing systems and duration, the rest of specimens were divided into following groups (n = 6): Youdent-20s group (Y20), Youdent-40s group (Y40), Youdent-60s group (Y60), Toboom-20s group (T20), Toboom-40s group (T40), and Toboom-60s group (T60). Additionally, a contour graph was applied for assessing the surface roughness of zirconia, scanning electron microscope (SEM) for observing surface topography, and X-ray diffraction analysis (XRD) for determining crystal structure of zirconia.

Results

The GR group had the highest roughness, and the roughness of the specimens polished for 20 s with different polishing systems was significantly higher than those polished for 40 s and 60 s with the same polishing systems. There were no significant difference between the Y20 and T20 groups, while the roughness of the specimens in both Y40 and Y60 groups was significantly higher than that of the T40 and T60 groups. And with the increasing polishing duration, the surface morphology of the specimen was gradually smooth and the morphology was gradually regular. Besides, the surface scratches of the T group were shallower than that of the Y group at the same polishing duration. The peak value of XRD profile of the specimen after grinding and polishing process was consistent with the baseline pattern of that the original specimen.

Conclusion

Glazing can reduce the surface roughness of the specimens. Besides, the polishing effect of Toboom (TOB) system (polishing duration = 60 s) is the best. And different polishing durations of TOB system have no significant effect on the crystal surface structure of the specimen.

Effect of finishing/polishing techniques and aging on topography, C. albicans adherence, and flexural strength of ultra-translucent zirconia: an in situ study

OBJECTIVE

To investigate the influence of different finishing/polishing techniques and in situ aging on the flexural strength (σ), surface roughness, and Candida albicans adherence of 5 mol% yttria-stabilized zirconia (ultratranslucent zirconia).

MATERIALS AND METHODS

A total of 120 zirconia bars (Prettau Anterior, Zirkonzahn) with dimensions of 8 × 2 × 0.5 mm were divided into 8 groups (n = 15) according to two factors: "in situ aging" (non-aged and aged (A)) and "finishing/polishing" (control (C), diamond rubber polishing (R), coarse grit diamond bur abrasion (B), and coarse grit diamond bur abrasion + diamond rubber polishing (BR)). Half of the samples from each group were subjected to a 60-day in situ aging by fixing the bars into cavities prepared in the posterior region of the base of complete or partial dentures of 15 patients. The samples were then subjected to the mini flexural (σ) test (1 mm/min). A total of 40 zirconia blocks (5 × 5 × 2 mm) were prepared and subjected to roughness (Ra) analyses and fungal adherence and complementary analyses (X-ray diffraction (XRD) and scanning electron microscopy (SEM)). The data of mean σ (MPa) and roughness Ra (μm) were statistically analyzed by two-way and one-way ANOVA, respectively, and Tukey's test. The Weibull analysis was performed for σ data. The fungal adhesion (Log CFU/mL) data were analyzed by Kruskal-Wallis tests.

RESULTS

For flexural resistance, the "finishing/polishing" factor was statistically significant (P = 0.0001); however, the "in situ aging" factor (P = 0.4458) was not significant. The non-aged (507.3 ± 115.7 MPa) and aged (487.6 ± 118.4 MPa) rubber polishing groups exhibited higher mean σ than the other techniques. The non-aged (260.2 ± 43.3 MPa) and aged (270.1 ± 48.8 MPa) bur abrasion groups presented lower σ. The coarse-grit diamond bur abrasion group (1.82 ± 0.61 µm) presented the highest roughness value (P = 0.001). Cell adhesion was not different among groups (P = 0.053). Group B presented the most irregular surface and the highest roughness Ra of 0.61 m.

CONCLUSIONS

The finishing of ultratranslucent zirconia might be preferably done with a diamond rubber polisher. Moreover, the protocols used did not interfere with Candida albicans adhesion.

CLINICAL RELEVANCE

Coarse-grit diamond burs might be avoided for finishing ultratranslucent monolithic zirconia, which might be preferably performed with a diamond rubber polisher.

Influence of Additive Firing on the Surface Characteristics, Streptococcus mutans Viability and Optical Properties of Zirconia

The purpose of this study was to observe whether the repetitive firing of dental zirconia caused changes in surface characteristics, S. mutans viability, and optical properties of zirconia. Dental zirconia blocks were sintered and randomly distributed into seven experimental groups: F0–F6. Except for F0, which only went through sintering, the additive firing was performed in order for F1–F6. Surface roughness, contact angle, S. mutans viability by fluorescence, and translucency parameter were measured. They were all highest after sintering (F0) and decreased after additive firings (F1–F6). The additive firing of zirconia after sintering decreased surface roughness, contact angle, S. mutans viability, and translucency. The number of firings after the first firing was not found to be critical in surface characteristics, S. mutans viability, and optical property. Changes in surface characteristics might have led to a decrease in S. mutans viability, while the change of translucency was not clinically significant. This implies that additive firing may prevent secondary caries under zirconia restorations, not compromising esthetic appearance.

Simulated clinical adjustment and intra-oral polishing of two translucent, monolithic zirconia dental ceramics: An in vitro investigation of surface roughness

OBJECTIVE

To assess the surface roughness and residual flaws in two translucent zirconia substrates following simulated clinical adjustment and intra-oral finishing/polishing.

MATERIALS AND METHODS

Specimens were prepared from two translucent (5Y-ZP/8Y-ZP) and one conventional (3Y-TZP) zirconia substrates (n = 84 p/g). Arithmetic mean roughness parameter (R_a) was determined for all experimental groups at four stages (n = 21 p/g): (1) as-sintered, (2) surface grinding using a zirconia cutting diamond bur, (3) polishing using 1-step, 2-step or 4-step intra-oral polishing kits, and (4) laboratory polishing/glazing. Scanning electron microscopy (SEM) was used to evaluate residual surface flaws. Data were statistically analysed using a two-way ANOVA test, multiple and pairwise comparisons were performed using a Bonferroni post hoc test.

RESULTS

R_a was significantly higher for as-sintered and ground 5Y-ZP/8Y-ZP compared to 3Y-TZP (p ≤ 0.001). Material type and polishing protocol had statistically significant effect on R_a (p < 0.001). The 4-step polishing resulted in the lowest R_a in 3Y-TZP/5Y-ZP (p ≤ 0.001). No significant differences were observed between different polishing protocols in 8Y-ZP (p≥0.655). Glazing significantly reduced R_a in all materials compared to other polishing protocols (p ≤ 0.001) except for the 4-step protocol in 3Y-TZP (p = 0.195). SEM revealed pronounced surface flaws in ground 5Y-ZP/8Y-ZP. Grinding of 3Y-TZP induced ductile material removal and thereby, minimal cohesive material loss. The 4-step polishing protocol resulted in the fewest and shallowest surface flaws in all groups. Glazing of 3Y-TZP resulted in the most homogenous surface contrary to 5Y-ZP/8Y-ZP.

CONCLUSIONS

The finest surface finish was achieved using the 4-step polishing protocol in all studied materials. This protocol might be inadequate however for polishing of ground 5Y-ZP/8Y-ZP as a result of the pronounced surface damage induced by the grinding process. The glazing of 5Y-ZP/8Y-ZP might not be as predictable as for 3Y-TZP.

CLINICAL SIGNIFICANCE

The higher susceptibility to surface damage, as a result of increasing dopant concentration, may render polishing of ground, translucent zirconia more complicated compared to the conventional 3Y-TZP counterparts.

Annealing and N2 Plasma Treatment to Minimize Corrosion of SiC-Coated Glass-Ceramics

To improve the chemical durability of SiC-based coatings on glass-ceramics, the effects of annealing and N₂ plasma treatment were investigated. Fluorapatite glass-ceramic disks were coated with SiC via plasma-enhanced chemical vapor deposition (PECVD), treated with N₂ plasma followed by an annealing step, characterized, and then immersed in a pH 10 buffer solution for 30 days to study coating delamination. Post-deposition annealing was found to densify the deposited SiC and lessen SiC delamination during the pH 10 immersion. When the SiC was treated with a N₂ plasma for 10 min, the bulk properties of the SiC coating were not affected but surface pores were sealed, slightly improving the SiC’s chemical durability. By combining N₂ plasma-treatment with a post-deposition annealing step, film delamination was reduced from 94% to 2.9% after immersion in a pH 10 solution for 30 days. X-ray Photoelectron spectroscopy (XPS) detected a higher concentration of oxygen on the surface of the plasma treated films, indicating a thin SiO₂ layer was formed and could have assisted in pore sealing. In conclusion, post-deposition annealing and N₂ plasma treatment where shown to significantly improve the chemical durability of PECVD deposited SiC films used as a coating for glass-ceramics.

Novel Coating to Minimize Corrosion of Glass-Ceramics for Dental Applications

The effect of a novel silicon carbide (SiC) coating on the chemical durability of a fluorapatite glass-ceramic veneer was investigated by examining weight loss and ion release levels. The hypothesis that this novel coating will exhibit significant corrosion resistance was tested. Inductively coupled plasma atomic emission spectrometer (ICP) was used for ion concentration determination and scanning electron microscopy (SEM) for surface morphology analyses. Samples were immersed in pH 10 and pH 2 buffer solutions to represent extreme conditions in the oral cavity. Analyses were done at 15 and 30 days. The SiC coated group demonstrated significant reduction in weight loss across all solutions and time points (p < 0.0001). Ion release analyses demonstrated either a marginally lower or a significantly lower release of ions for the SiC-coated disks. SEM analysis reveals planarization of surfaces by the SiC-coated group. The surfaces of coated samples were not as corroded as the non-coated samples, which is indicative of the protective nature of these coatings. In conclusion, SiC is a novel coating that holds promise for improving the performance of ceramic materials used for dental applications.

Evaluation of the effect of tooth polishing on color stability after in-office bleaching treatment

Abstract Introduction One of the most commonly used corrective methods for staining teeth is tooth bleaching. However, subclinical alterations may occur in the micromorphology of dental tissues during the bleaching procedure, such as increases in porosity and surface roughness. Consequently, dental enamel may become more permeable and susceptible to staining. Objective To evaluate the influence of tooth polishing after in-office bleaching treatment on color stability. Material and method Thirty-three extracted human molars were used. The teeth were cut in the mesiodistal direction to obtain two samples per tooth (total of 66). The samples were randomly divided into six groups (n=11). Before and after the bleaching treatment, the lightness of the samples and change in lightness (∆L) were determined with a digital spectrophotometer (Easy Shade). The samples were bleached with 35% hydrogen peroxide (three sessions weekly). Three groups were submitted to polishing with felt discs and polishing paste after each session. To simulate the oral conditions during the consumption of colored beverages, the samples were submitted to alternating cycles of immersion in staining solutions (coffee, red wine, and Coca Cola). Result Polishing resulted in an increase of mean lightness of 4.49 in the red wine group, 2.73 in the coffee group, and 4.08 in the cola group. The difference was significant in the red wine group (p<0.022), but not in the coffee or cola group. Conclusion Polishing after in-office bleaching using felt discs and polishing paste can reduce the degree of pigment impregnation in patient with red wine rich diet.